Valves for controlling fluid flow generally include a flow passage extending between an inlet port and an outlet port in a valve housing and a valve element and a valve seat disposed within the flow passage. The valve element is movable between a first position wherein fluid flow is permitted through the passage from the inlet end to the outlet end and a second position wherein the valve element sealingly engages the valve seat substantially blocking fluid flow through the passage.
Moving contact of the valve element with the valve seat causes wear of the valve seat over an extended period of time. Consequently, it is desirable to provide a valve seat which is removable from the valve housing so that the valve seat can be replaced without the need to replace the entire valve housing. Several types of removable valve seat configurations are known in the prior art. In one such configuration, a threaded valve seat may be received by a complementary, threaded bore defined within the valve housing so that the valve seat can be unscrewed and removed from the valve housing when it fails to provide an adequate seal with the valve element in the second or closed position described above. These so-called "screwed in" seat rings are inexpensive, but they can be difficult to replace because the threaded parts, which are constantly submerged in fluid, tend to corrode. As a result, special removal tools are required to remove the threaded valve seat from the valve housing making the removal procedure time-consuming and cumbersome.
A second suggested valve seat configuration employs retaining structure to secure the valve seat in a predetermined position within the valve housing. Removal of these so-called "retained ring" valve seats is not encumbered by corrosion, but the retaining structure is disposed within the fluid flow passage and thus undesirably obstructs fluid flow and increases turbulence within the passage thereby resulting in a decrease in the flow capacity capability of the valve.
Accordingly, it is desired to provide a valve, such as a globe-style valve, having a removable valve seat that is inexpensive and easily replaceable and does not substantially increase turbulence in fluid flowing in the passage.